There have been developed various porous materials for use in industry and government for chemical separations, processing and monitoring, environmental cleanup and remediation, energy efficiency and conservation. Porous materials used in these applications include foams, filters, membranes, absorbents, ion exchange resins, molecular sieves, zeolites, catalyst supports, sensors and electrodes. Polymeric foams have found limited use in several of the above-mentioned applications because of the difficulty of controlling foam morphology at the sub-micron level using conventional foam producing techniques.
Efforts have been made to control porosity in rigid-rod hypercross-linked polymers at the nanometer level using low temperature condensation reactions or sol-gel processing techniques. While some successes are noted, the starting materials can be expensive or difficult to synthesize and the cross-linking reactions are cumbersome and not amenable to large scale preparations.
Highly cross-linked polystyrenes with extraordinarily high surface areas which have a high enough density of rigid cross-linking to prevent polymeric network collapse have been developed. Although these polystyrenes swell in thermodynamically unfavorable solvents, absorb dyes and hydrocarbons, and readily absorb gases, these polystyrenes are in some ways not the best materials for separation technologies. The nanostructures of these highly cross-linked polystyrenes cannot easily be varied since the pore sizes and volumes are determined for the most part by the length and structure of the cross-linking agent. The flexible backbone of the polystyrene starting material requires that rigid cross-linking agents be employed in order to obtain true nanoporosity in the bulk material, thus limiting choices of design and properties. These hypercross-linked polystyrenes possess high glass transition temperatures and high decomposition temperatures. These undesirable characteristics prevent use of the polymers in harsh environments.
There is still a need for easily tailorable, nanoporous, rigid, hypercross-linked polymeric materials. There is a need for such polymeric materials which can be made simply from relatively inexpensive starting materials.